Numerical and experimental investigations on supercritical-pressure flow turbulence and heat transfer enhancement of hydrocarbon fuel in pin-fin regenerative cooling channels

Thermal protection is a crucial issue for Combined-Cycle Engines (CCE) in advanced propulsion systems. Uneven flow distribution and localized heat transfer deterioration limit the application of parallel cooling channels in CCE under multimodal operating conditions. The pin-fin structure presents a promising approach for the next-generation regenerative cooling channel design. The flow and supercritical-pressure heat transfer behavior of hydrocarbon fuel flowing in pin-fin regenerative cooling channels were investigated in this work via large eddy simulations and experiments. Detailed analyses of flow turbulence, vortex structures, and thermal fields were conducted for three distinct pin-fin geometries (circular, elliptic, and square). Results indicated that the square pin-fin configuration exhibits the highest thermal performance factor, with a Thermal Performance Factor 3.5 times greater than that of the iso-parallel channel and reduces the wall temperature by ∼40%. The heat transfer is enhanced by impingement cooling resulting from the horseshoe vortex near the leading edge of the fin and the unsteady Kármán vortex after the flow separation point, which increases the turbulent intensity of the shear layer. The elliptical pin-fin exhibits comparable heat transfer to the circular one while inducing only 19% of the pressure drop. Ground-based direct-connect thermal test at a simulated flight Mach number of 6 was conducted to verify the heat transfer efficiency of the pin-fin cooling plates. Experiment results demonstrated that the average temperature on the heating surface of the square pin-fin regenerative cooling plate can be reduced up to 27% compared to that of the iso-parallel cooling plate, while the non-uniform circumferential temperature distribution caused by uneven flow distribution can also be significantly mitigated. Effects of coolant mass flow rate, combustion equivalence ratio, and coolant pressure on heat transfer efficiency decrease successively. This work provides quantitative design guidelines and fundamental insights for implementing high-efficiency, lightweight pin-fin regenerative cooling channels in advanced CCE.